What I like about Columbo is watching Columbo and the suspect interact. This is why I can watch an episode so many times.
Playback had some really good interaction between Columbo and Harold. Watching Harold's pent up anger and frustration was fun, especially when confronted by an innocent person just doing his job without a care in the world, meanwhile Harold has all this guilt, anger and frustration boiling inside.
One of the best examples of this was Death Lends A Hand.
As for the doors opening when the gun was shot, in the surveillance tape you can see the front door open while the Margret falls to the ground. And there's a goof on the tape.... there is a puff of gunshot smoke that comes out in the upper left hand corner of the surveillance tape....there's no way the gun was shot from behind the camera mounted up on the wall!